Vacuum generation in the pocket of a single wire dryer group

ABSTRACT

In a single wire dryer group, a paper web travels on one side of a support belt over a first dryer cylinder, then over a guide roll, then over a second dryer cylinder moving through the dryer group. A pocket is defined between the two adjacent dryer cylinders and the guide roll between them. To develop a vacuum within the pocket in the vicinity of the outer surface of the first dryer cylinder, there is a sealing ledge at the support belt at the first dryer cylinder. The sealing ledge is fastened to a sealing ledge support. An air guide surface on the side of the sealing ledge support away from the pocket is curved first in a direction toward the bottom of the pocket and then away from the pocket around axes above the air guide surface. Toward the second cylinder, the sealing ledge support defines an air ejector nozzle. A first air flow induced on the first dryer cylinder is deflected upward around and past the ejector nozzle by the curvature of the air guide surface. A second air flow traveling along the support belt past the second dryer cylinder is induced to pass through and exits through the nozzle. The first and second air flows are then combined at the outlet from the ejector nozzle.

BACKGROUND OF THE INVENTION

The present invention relates to a single-wire dryer group of a papermaking machine and particularly to air deflection means within a pocketof the dryer group for generating a vacuum there.

A single wire dryer group has a plurality of dryer cylinders. The web tobe dried moves over the cylinders in sequence. A respective guide rollis disposed between each two cylinders in the path of the web. A poroussupport belt, e.g. a wire screen or wire, carries the web to be driedfrom one dryer cylinder to a succeeding guide roll and then to the nextdryer cylinder in the path of the web through the dryer group. The webis carried on the side of the support belt that places the web in directcontact with the dryer cylinders and that also places the web on theoutside of the support belt as it passes over the guide rolls. Featuresof such a single wire dryer group are disclosed in U.S. Pat. No.4,359,828, particularly FIG. 7, for example. Such a dryer is preferablypart of a paper making machine.

In a single-wire dryer group, the web to be dried, which is a web ofpaper, is guided continuously by the porous support belt and is presseddirectly against the dryer cylinders. The web and the support belttravel, for instance, from a first dryer cylinder jointly over theshortest possible path to the following guide roll and from the latterback to a second dryer cylinder and then over a second guide roll to athird dryer cylinder, etc. The volume bounded by two neighboring dryercylinders and the guide roll between them is called the pocket.Typically, the guide roll axis is off an imaginary line between the axesof the two cylinders and the pocket is to the side of that line towardthe guide roll axis.

The guide roll can be arranged in a symmetrical arrangement at an equaldistance from each of the two adjacent dryer cylinders. However, anasymmetric arrangement is known in which the smallest possible distanceis provided between the first dryer cylinder and the guide roll while asubstantially greater distance is provided between the guide roll andthe second dryer cylinder.

Upon the web leaving the first dryer cylinder, it is essential that theweb not adhere to the cylinder, but that the web instead be drawnagainst the support belt by a vacuum produced in the pocket. Also, theweb must be drawn against the support belt in the wrapping zone aroundthe guide roll, in opposition to the centrifugal force acting on theweb. This can be achieved, for instance, by producing the guide rollwith circumferential grooves into which the vacuum produced in thepocket is propagated. Alternatively, the guide roll is formed as asuction roll, with or without an inner stationary suction box, and theshell of the roll is perforated. It is also important that the web bedependably held against the support belt along the path of the web fromthe guide roll to the second dryer cylinder by the vacuum prevailing inthe pocket.

In FIG. 7 of U.S. Pat. No. 4,359,828, production of a vacuum in thepocket is attempted by the following measures. A first sealing ledge,which is fastened to a sealing ledge support, is arranged in the pocketin the vicinity of the outer surface of the first dryer cylinder.Similarly, a second sealing ledge, which is also fastened to a sealingledge support, is arranged in the vicinity of the outer surface of thesecond dryer cylinder. The two sealing ledge supports are curved in sucha manner that they deflect the flow of air that is induced by thetraveling support belt on the first dryer cylinder into the direction inwhich the support belt travels over the second dryer cylinder. Togetherwith an additional flow guide wall, the two sealing ledge supports forma flow channel which has an ejector like opening through which air isdrawn upward out of the pocket. In this way, a certain vacuum canprevail in the pocket. The strength of this vacuum is, however,insufficient in actual practice.

SUMMARY OF THE INVENTION

The object of the invention is to develop the known arrangement in asingle wire dryer group to produce a substantially greater vacuum thanthe level of vacuum previously present in the pocket.

In a single wire dryer group, a paper web travels on one side of asupport belt directly over a first heatable dryer cylinder, then outsidethe support belt over a guide roll, and then over a second dryercylinder. A pocket is defined between the two adjacent dryer cylindersand the guide roll between them. A vacuum is to be developed within thepocket. In the vicinity of the outer surface of the first or upstreamdryer cylinder, there is a sealing ledge at the support belt. Thesealing ledge is fastened to a sealing ledge support that extendsbetween the dryer cylinders and is above the guide roll. An air guidesurface is defined on the sealing ledge support at its side away fromthe pocket and away from the guide roll. The sealing ledge support airguide surface is curved around axes above that surface, first in adirection toward the bottom of the pocket and then away from the bottomof the pocket, that is first generally in the direction along the pathof the support belt past the first cylinder and toward the bottom of thepocket, and then toward the second cylinder and generally in thedirection along the path of the support belt past the second cylinder.The sealing ledge support defines an air ejector nozzle at the seconddryer cylinder. Air flow induced on the support belt at the first dryercylinder is deflected off the support belt, upward around and past theejector nozzle by the curvature of the sealing ledge support air guidesurface. A second air flow that travels along the support belt past thesecond dryer cylinder is induced to pass through and exits through thenozzle. The first and second air flows are then combined at the outletfrom the ejector nozzle.

In the invention, only a single sealing ledge is provided, and it islocated on the shell of the first dryer cylinder. Thus, only a singlesealing ledge support is necessary. Furthermore, an ejector like openingserving for the removal of air from the pocket is no longer formedbetween two sealing ledge supports, but rather is formed between thesingle sealing ledge support and the outer surface of the second dryercylinder which is covered by the support belt. The invention uses theflow of air which the support belt induces at its normally highoperating speeds (about 1,000 to 2,000 m/min) over the relatively shorttravel path of the support belt from the guide roll to the second dryercylinder. This flow of air is referred to below as the "second airflow", while the flow of air induced by the support belt on the firstdryer cylinder is referred to below as the "first air flow".

The two air flows are combined by an ejector like opening, which is alsoreferred to as an "ejector nozzle", between the sealing ledge supportand the shell of the second dryer cylinder, and particularly the supportbelt passing over the second dryer cylinder. In this connection, atleast the second air flow, which is induced by the pumping action of thesupport belt or wire traveling from the guide roll to the second dryercylinder, produces a vacuum in the pocket of an amount which in manycases is sufficient for dependable operation of the single wire dryergroup.

Supporting measures for attaining this goal may be:

A. Omission of the additional flow guide wall which was previouslypresent and which would tend to exert a braking action on the first airflow.

B. A flow favoring shape of the sealing ledge and of the sealing ledgesupport so that the first air flow is braked as little as possible.

C. In accordance with a further concept of the invention, accelerationof the first air flow can even be obtained on the sealing ledge support,by increasing the curvature of the air flow guide surface of the sealingledge support in the direction of flow. In other words, the radius ofcurvature of the flow guide surface decreases in the direction of flow.In this case, it is possible for the flow guide surface to have a flatinitial part in the region of the sealing ledge. The acceleration of thefirst air flow produces a suction effect at the ejector nozzle on theair present in the pocket, increasing the vacuum produced there.

In a further embodiment of the invention, provision is made to minimizeproblems which may arise in cases of disturbance, e.g. in the event of aweb break resulting in the danger that the web might wind itself on oneof the dryer cylinders or to minimize problems in the event that thesupport belt tears. The sealing ledge support is swingably mounted sothat the sealing ledge can be moved away from the first dryer cylinder.At the same time, the ejector like opening between the sealing ledgesupport and the second dryer cylinder is increased in size. As a result,e.g. in the event of a web break, the danger that the support belt tearsis minimized. If, nevertheless, in a certain event, the support beltshould tear, the danger of damage to the dryer cylinders and to theguide roll is avoided. Furthermore, the introduction of a new supportbelt is facilitated. The sealing ledge support can be made automaticallyswingable by unintended contact of the support belt with the sealingledge or with the sealing ledge support when both are supportedswingably on a support.

The above described features can also be employed in the case of asealing ledge support which is developed without means for removing airfrom the pocket.

It is evident that a moveable sealing ledge support must be supported ona support beam which extends transversely to the direction of travel ofthe web through the pocket. In order to avoid disturbances, largedistances are provided between the sealing ledge support and the travelpath of the support belt. On the other hand, a wall of the support forthe sealing ledge support can be closely adapted to the outer surface ofthe guide roll and can be arranged at a slight distance from it.

Other objects and features of the invention are disclosed with referenceto one embodiment of the invention which is described below withreference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a portion of a single wire dryer group havingthe sealing ledge provided in a pocket.

FIG. 2 is a diagrammatically simplified view, shown on a reduced scaleas compared with FIG. 1, and seen in the direction of the arrow II ofFIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows two dryer cylinders 11 and 12 of a single wire dryer groupof a paper making machine. The cylinders are arranged one after theother in a row and also in the path of a web through the dryer group. Aguide roll 10 is present between the cylinders. A support belt 9travels, together with the web of paper to be dried, from the firstdryer cylinder 11 to the guide roll 10 and from the latter to the seconddryer cylinder 12. The space between the cylinders, which is also partlyclosed by the guide roll, is referred to as a "pocket" 13. In theembodiment shown, the two dryer cylinders 11 and 12 are arrangedalongside of each other and have rotation axes which are joined by animaginary line. The guide roll 10 lies below the dryer cylinders, withthe rotation axis of the guide roll disposed below the line joining thecylinder axes. However, other arrangements of the two dryer cylindersand the guide roll between them are possible. For instance, the guideroll 10 may be above the dryer cylinders, or the dryer cylinders may beone above the other, so that the guide roll lies to the right or theleft of and alongside the dryer cylinders.

The guide roll 10 is shown diagrammatically as a non-aspirated,non-suction roll having a smooth roll shell. However, the roll shellcould also be provided with circumferential grooves or withperforations. The guide roll could also be developed as a suction roll,with or without an internal stationary suction box, and the roll shellwould also then be provided with perforations.

A sealing ledge 31 is arranged in the pocket in the vicinity of theouter surface of the first dryer cylinder 11. The ledge 31 is fastenedto ap1776Xsealedge support 30. The upper side of the support 30 (as seenin the embodiment shown), i.e. the side facing out of the pocket, has anair guide surface 29 which is curved convexly toward the bottom of thepocket, i.e. it has axes of curvature above the air guide surface andout of the pocket. The air guide surface extends from the upper side ofthe sealing ledge 31 at the first dryer cylinder to close to the outersurface of the second dryer cylinder 12 which is covered by the supportbelt. The guide surface 29 terminates near the second dryer cylinder ina section of the surface 29 which is approximately parallel to the outersurface of the second dryer cylinder. At least this end section of theair guide surface 29 is formed by a relatively thin plate which is partof the sealing ledge support 31. Together with the outer surface of thesecond dryer cylinder 12 and particularly with the support belt passingover the second dryer cylinder, the sealing ledge support 31 forms anejector nozzle 28 there.

The curvature of the air guide surface 29 increases in the direction offlow. In the initial air flow region close to the sealing ledge 31,there is a relatively large radius of curvature R, while in the finalsection toward the second cylinder 12, there is a relatively smallradius of curvature r of the air guide surface.

The arrangement described above operates in the following manner:

The support belt 9 travels on its path over the first dryer cylinder 11.The belt carries along with it, in known manner, an air boundary layeror, in other words, it induces a first air flow 21 which is downwardinto the pocket. The first air flow 21 is deflected by the sealing ledge31 and by the curved sealing ledge support 30 to be redirected in thedirection in which the support belt 9 travels over the second dryercylinder 12, i.e. outward from the pocket. The first air flow 21 istherefore substantially prevented from penetrating to the bottom of thepocket 13. It is instead removed from the pocket again. The second airflow 22 which is induced by the support belt 9 on its path from theguide roll 10 to the second dryer cylinder 12 is transported outwardfrom the pocket. In cooperation with the seal provided by the lateralpocket covers 33, which are described below, a reduced air pressure,partial vacuum condition is produced in the pocket 13. This vacuumcauses the web of paper which is to be dried to dependably adhere to theporous support belt 9 in the region of the straight path of travel ofthe support belt between cylinder 11 and guide roll 10, as well as inthe region of the path between guide roll 10 and cylinder 12.

The vacuum can be further increased by increasing the curvature of theair guide surface 29 in the direction of flow. This accelerates thefirst air flow 21. This also increases the speed of the second air flow22 and thus increases the vacuum produced in the pocket 13.

The sealing ledge support 30 is mounted by several links 27 which arearranged in pairs at opposite axial ends of the support. The links areswingable on a box shaped support 26 which extends transversely to thedirection of travel of the web through the pocket 13. The support 26 isfastened, as shown in FIG. 2, on rigid parts 25 of the housing. Thesealing ledge support 30 is furthermore articulately connected by atleast one connecting rod 23 to at least one crank, drive disk 24, or thelike. The latter is fastened on a shaft 32 which extends parallel to thesupport 26 and is mounted rotatably on it at bearings 34. This enablesthe sealing ledge 31 and the sealing ledge support 30 to be swung backand forth between two positions. Their normal operating position isshown in solid line in the drawing. Their other position is shown indash-dot lines in FIG. 1 and is designated 31' and 30'. In the latterposition, the distances between sealing ledge/sealing-ledge support andthe dryer cylinders 11 and 12 is substantially greater than in theoperating position. The distances a, b between the side walls of thesupport 26 and the travel paths of the support belt 9 are at all timesrelatively large, as can be noted from FIG. 1.

Lateral covers 33 which limit the pocket 13 at its two axial ends, i.e.on the operator and the driven sides of the paper making machine, helpto maintain the vacuum produced in the pocket because they prevent thelateral drawing-in of infiltrating air.

Although the present invention has been described in relation to aparticular embodiment thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claimed is:
 1. A single wire dryer group comprisinga plurality of dryer cylinders in a path of a web to be dried through the dryer group, a respective guide roll between two neighboring ones of the dryer cylinders in the dryer group, such that a support belt carries the web alternately over a first one of the dryer cylinders, then over a neighboring one of the guide rolls, then over a second one of the dryer cylinders along the path of the web through the dryer group; the first and the second dryer cylinders and the guide roll between the dryer cylinders forming and defining a pocket; a sealing ledge support, support means for supporting the sealing ledge support in the pocket, a sealing ledge supported on the sealing ledge support and located near the outer surface of the first dryer cylinder, and the sealing ledge and the sealing ledge support together having an air guide surface facing out of the pocket and positioned so as to deflect over the sealing ledge and onto and over the sealing ledge support a first air flow that is being moved by the support belt traveling over and past the first dryer cylinder; the air guide surface being shaped to deflect the first air flow substantially in a direction over which the support belt is traveling over the second dryer cylinder; the sealing ledge support being so shaped and spaced from and cooperating with the support belt passing over the second dryer cylinder as to form between them an ejector nozzle for a second air flow traveling out of the pocket with the support belt, whereby the first air flow flows over the sealing ledge support past the ejector nozzle while the second air flow flows over the support belt past the second dryer cylinder, and the second air flow is induced out of the pocket by the traveling support belt passing over the second dryer cylinder for producing a vacuum in the pocket, and the sealing ledge support being so disposed with respect to the second dryer cylinder and the ejector nozzle that the first air flow over the sealing ledge support and the second air flow through the nozzle combine at the outlet of the ejector nozzle.
 2. The single wire dryer group of claim 1, wherein the first and the second dryer cylinders have respective rotation axes, and the guide roll has a rotation axis that is off to one side of a line joining the rotation axes of the first and second dryer cylinders, and the pocket being toward the one side of the line joining the axes of the dryer cylinders between the first and second dryer cylinders and the guide roll.
 3. The single wire dryer group of claim 1, further comprising a web support belt passing over the first dryer cylinder, then over the one guide roll and then over the second dryer cylinder, the support belt supporting the web to be dried on the side of the belt such that the web is in direct contact with the first and second dryer cylinders while the support belt passes between the web and the guide roll.
 4. A single wire dryer group comprisinga plurality of dryer cylinders in a path of a web to be dried through the dryer group, a respective guide roll between two neighboring ones of the dryer cylinders in the dryer group, such that a support belt carries the web alternately over a first one of the dryer cylinders, then over a neighboring one of the guide rolls, then over a second one of the dryer cylinders along the path of the web through the dryer group; the first and the second dryer cylinders and the guide roll between the dryer cylinders forming and defining a pocket; a sealing ledge support, support means for supporting the sealing ledge support in the pocket, a sealing ledge supported on the sealing ledge support and located near the outer surface of the first dryer cylinder, and the sealing ledge and the sealing ledge support together having an air guide surface facing out of the pocket and positioned so as to deflect over the sealing ledge onto and over the sealing ledge support a first air flow that is being moved by the support belt traveling over and past the first dryer cylinder; the air guide surface being curved convexly into the pocket and around axes above the air guide surface to deflect the first air flow substantially in a direction over which the support belt is traveling over the second dryer cylinder; the sealing ledge support being so shaped and spaced from and cooperating with the support belt passing over the second dryer cylinder as to form between them an ejector nozzle for a second air flow traveling out of the pocket with the support belt, whereby the first air flow flows over the sealing ledge support past the ejector nozzle while the second air flow flows over the support belt past the second dryer cylinder, and the second air flow is induced out of the pocket by the traveling support belt passing over the second dryer cylinder for producing a vacuum in the pocket, and the sealing ledge support belt is so disposed with respect to the second dryer cylinder and the ejector nozzle that the first air flow over the sealing ledge support and the second air flow through the nozzle combine at the outlet of the ejector nozzle.
 5. A single wire dryer group comprisinga plurality of dryer cylinders in a path of a web to be dried through the dryer group, a respective guide roll between two neighboring ones of the dryer cylinders in the dryer group, such that a support belt carries the web alternately over a first one of the dryer cylinders, then over a neighboring one of the guide rolls, then over a second one of the dryer cylinders along the path of the web through the dryer group; the first and the second dryer cylinders and the guide roll between the dryer cylinders forming and defining a pocket; a sealing ledge support, support means for supporting the sealing ledge support i the pocket, a sealing ledge supported on the sealing ledge support and located near the outer surface of the first dryer cylinder, and the sealing ledge and the sealing ledge support together having an air guide surface facing out of the pocket and positioned so as to deflect over the sealing ledge onto and over the sealing ledge support a first air flow that is being moved by the support belt traveling over and past the first dryer cylinder; the air guide surface being shaped to deflect the first air flow substantially in a direction over which the support belt is traveling over the second dryer cylinder; the sealing ledge support being swingably mounted on the support means to enable adjustment of the distance between the sealing ledge and the first dryer cylinder and to enable adjustment of the distance between the sealing ledge support and the second dryer cylinders; the sealing ledge support being so shaped and spaced from and cooperating with the support belt passing over the second dryer cylinder as to form between them an ejector nozzle for a second air flow traveling out of the pocket with the support belt, whereby the first air flow flows over the sealing ledge support past the ejector nozzle while the second air flow flows over the support belt past the second dryer cylinder, and the second air flow is induced out of the pocket by the traveling support belt passing over the second dryer cylinder for producing a vacuum in the pocket, and the sealing ledge support belt is so disposed with respect to the second dryer cylinder and the ejector nozzle that the first air flow over the sealing ledge support and the second air flow through the nozzle combine at the outlet of the ejector nozzle.
 6. This single wire dryer group of claim 4, wherein the radius of curvature of the air guide surface gradually decreases in the direction of the first air flow over the air guide surface toward the second dryer cylinder.
 7. The single wire dryer group of claim 5, wherein the swingable mounting for the sealing ledge support yieldably supports the sealing ledge support such that contact of the support belt with one of the sealing ledge and the sealing ledge support swings the sealing ledge support to increase the distances between the contacting parts.
 8. The single wire dryer group of claim 1, wherein the sealing ledge support has a section which is adjacent to and approximately parallel with the outer surface of the second dryer cylinder. 